RecyclerView scrolling to bottom of page doesn't trigger .addOnScrollListener's canScrollVertically

Question

I'm trying to implement a skipping feature in my vertical recyclerview. When a user clicks a button, the recyclerView will scroll all the way to the bottom and trigger an API call. Right now to check if the user is at the bottom of the screen, I am using .addOnScrollListener on my recyclerview.

mGridRecycler.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);

                //SCROLL_STATE_IDE prevents repeated calls from happening
                // when near bottom of screen and slightly scroll up a bit
                if(!mGridRecycler.canScrollVertically(1) && newState==RecyclerView.SCROLL_STATE_IDLE){
                    Log.d(TAG, "onScrollStateChanged: CALLED WTF");
                    mActivity.getNextPageGridView();
                }
            }
        });

And to implement the skipping feature to the last item, I am using this method on a button:

mGridRecycler.scrollToPosition(mList.size() - 1);

It skips to the last item, however the API call is not triggered because the if-statement is not called. Anyone know what I can make it work successfully?

I did not understand is the api call not working or the if condition inside of the onScrollStateChanged is always false? — DemoDemo, Feb 21 '20 at 17:19
The if condition is not called even though I am skipping to the bottom of the page and can not scroll anymore. — DIRTY DAVE, Feb 21 '20 at 17:22
@harrytmthy Yes it does. Only when trying to skip to the bottom of the page doing it programmatically, it doesn't work — DIRTY DAVE, Feb 24 '20 at 12:45
@davids. Good. Can you update your question and show me your `if-statement` which triggers the API call? I am really sure that is the problem. — Harry Timothy, Feb 24 '20 at 14:34

score 2 · Accepted Answer · answered Feb 26 '20 at 06:19

2

RecyclerView does not know how LayoutManager will handle the scroll.
You'll only receive a call to onScrolled if first and or last child position changes after a layout, you're not gonna get onScrollStateChanged callback.

What should you do?

Alternatively you can use smoothScrollToPosition(..) method, OR override onScrolled method, OR make a request to your API right after the skip button click, which is the best solution for your scenario.

answered Feb 26 '20 at 06:19

Tiko

990
7
18

I changed it to ```.smoothScrollToPosition``` and the API call is now working when I skip. Thanks for explaining. – DIRTY DAVE Feb 28 '20 at 21:43

score 0 · Answer 2 · edited Nov 29 '21 at 09:18

0

It will not scroll to the end of your layout if your content layout had a top margin or your item view have margin. I don't remember exactly but try to remove all margin of itemview and contentview. I solved the problem with a little hack, adding an empty view to the end of the LinearLayout earlier in my project.

edited Nov 29 '21 at 09:18

Nimantha

6,405
6
28
69

answered Feb 26 '20 at 07:23

Thành Hà Văn

481
2
9

score 0 · Answer 3 · answered Feb 27 '20 at 10:40

0

Recylerview scrolling is very fast so try to give a delay of 1 sec using handler or you can also use

recyclerView.post(() -> mGridRecycler.scrollToPosition(mList.size() - 1);

answered Feb 27 '20 at 10:40

Rajendra Dabhi

157
9

score 0 · Answer 4 · edited Nov 29 '21 at 09:20

In order to properly implement an auto smooth scrolling you need to do the following:

Declare a scroll speed constant:

companion object {
    const val SMOOTH_SCROLL_SPEED = 100f
}

Create a global SmoothScroller param:

private lateinit var smoothScroller: SmoothScroller

In your init method: Initialize the SmoothScroller object:

smoothScroller = object : LinearSmoothScroller(context) {
    override fun getVerticalSnapPreference(): Int {
        return SNAP_TO_START
    }

    override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics?): Float {
        displayMetrics?.let {
            return SMOOTH_SCROLL_SPEED / it.densityDpi
        }
        return super.calculateSpeedPerPixel(displayMetrics)
    }
}

Create this method and call it whenever you wish to smoothScroll to any position in the list:

open fun smoothScroll(position: Int) {
    smoothScroller.targetPosition = position
    yourRecycleView.layoutManager.startSmoothScroll(smoothScroller)
}

RecyclerView scrolling to bottom of page doesn't trigger .addOnScrollListener's canScrollVertically

4 Answers4